The invention relates to the general field of magnetic disk recording with particular reference to write heads.
As the recording density of magnetic disk drives has been pushed to beyond 50 Gbits/in2, it has become essential to be able to manufacture extremely small features. These densities require the read and write element widths to be smaller than 0.15 and 0.20 microns, respectively. At 100 Gbits/in2, their width will be even smaller, approximately 0.10 and 0.13 microns. Conventional photolithography is quickly running out of its capability to handle such small dimensions.
While other technique such as E beam lithography are being developed to meet the challenge, an approach that does not require a radical change in the imaging system is to be preferred. For example, the xe2x80x9cRELACSxe2x80x9d process has been developed to achieve small write head dimensions. This process is in two steps. First, as shown in FIG. 1, substrate 11 (which will serve as the bottom pole) is coated with non-magnetic write gap layer 12. Photoresist layer 13 is then laid down and patterned to form an opening whose width 15 is greater than the intended final width. Then, second photoresist layer 22 is laid down, as shown in FIG. 2, followed by a baking step. This initiates cross linking to begin at the resist 13/resist 22 interface. As long as heat is supplied, cross linking continues, moving outwards from the original interface into the bulk of resist 22.
By controlling the bake time, the thickness of cross linked layer 21 can be controlled so that, when the resist is developed, layer 21 remains and, as seen in FIG. 3, a new opening having a lesser width 35 has been formed.
In practice, the rate at which the cross linked layer grows depends, not just on bake time and temperature, but also on other parameters such as development history, impurity content, etc. so can be more difficult to control than the above description might suggest. The present invention takes a different approach to solving this problem, as we will disclose below.
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 6,289,578 B1, Kamijima shows a write head process/structure without using a dry etch process. Rottmayer, in U.S. Pat. No. 5,809,637, discloses a method to make a magnetic head assembly with a write Pole/shield structure while Matsukuma (U.S. Pat. No. 6,303,392 B1) shows an etch process for making write poles. U.S. Pat. No. 6,328,859 B1 (Hsiao et al.) discloses a method for making pole tips and U.S. Pat. No. 6,178,065 B1 (Terunuma et al.) shows a related patent including a write head process.
It has been an object of at least one embodiment of the present invention to provide a process for forming a write head for use in a magnetic disk storage system.
Another object of at least one embodiment of the present invention has been that said process be compatible with existing optical photolithography.
Still another object of at least one embodiment of the present invention has been that said write head have a track length that is no greater than about 0.2 microns.
A further object of at least one embodiment of the present invention has been that said process be applicable to any structure that requires a very narrow mid-section.
These objects have been achieved by first forming on the bottom pole of the write head a cavity in a layer of photoresist, using conventional means. A seed layer of non-magnetic material is electrolessly laid down, following which a second layer of photoresist is deposited and patterned to form a second cavity that symmetrically surrounds the first one, thereby forming a mold around it. Ferromagnetic metal is then electro-deposited in this mold to form the top magnetic pole. Following the removal of all photoresist and a brief selective etch of the bottom pole, an extremely narrow write head is obtained.